Cancer is one of the most common diseases worldwide. Biomarkers play a key role in cancer diagnosis and prognosis. Determining the presence of and/or quantities (relative amounts and/or absolute amounts) of multiple biomarkers are useful for accurate prediction and prognosis of cancers, and survival rate may depend at least in part on targeted therapy based upon accurate detection and quantification, wherein quantification comprises determining the size of a mass peak and correlating it with the amount of particular biomarkers. For example, in breast cancer, the relative abundances of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her2) biomarkers correlates to the patient's chances of surviving five or more years.
Immunohistochemistry (IHC) has been a major diagnostic tool to identify therapeutic biomarkers and to subclassify cancer patients. Conventional IHC methods using optical imaging are suitable for detecting one or more targets within a sample (e.g., a tissue sample). However, IHC methods cannot provide accurate quantitative results for the detected targets. Typically, only certified medical personnel are sufficiently skilled to evaluate a subject's diagnosis and prognosis based upon IHC optical imaging results. Currently, there is no suitable IHC platform for quantitative multiplexed assays useful for assessing cancers and determining personalized cancer therapy.
A number of methods have been developed for detecting and imaging biomolecules, such as nucleic acids and proteins. Nucleic acids, for example, may be analyzed using labeled probe molecules. The labels are detected to determine whether specific binding or hybridization has taken place. Various probe labeling methods are known, including radioactive atoms, fluorescent dyes, luminescent reagents, electron capture reagents and light absorbing dyes. Each of these methods has features suitable for certain applications, but there also are inherent limitations to each such method.
Mass spectrometry has been increasingly used for bioanalytical analyses. Mass spectrometry his well suited for multiplexing because mass differentiation allows many simultaneous detection channels. However, complex biomolecules, such as DNA, have complex mass spectra and may be difficult to detect in a matrix due to relatively poor sensitivity.